This invention relates to cathodic sputtering and, more particularly, to triode apparatus for cathodic sputtering of semiconductor devices.
Cathodic sputtering is an advantageous method for the fabrication of many types of semiconductor devices including particularly monolithic integrated circuits. It is used in both the deposition mode and in the etching mode particularly for making metallic interconnection patterns. However, in both modes a problem arises in that contamination of the semiconductor device surfaces and surface films thereon is likely to occur because the sputtering ions impinge upon surfaces other than the designated target material. This problem is more serious in triode sputtering systems than in those of the simpler diode type because of the additional fixturing of plasma confinement and target and workpiece supports. However, triode systems are of particular interest because they can be used on surface sensitive devices, such as insulated gate field effect devices which are subject to unannealable radiation damage in a diode system environment. In the triode system having a supported discharge, voltage and current can be independent, and operation in a high current-low voltage mode is possible, thus avoiding the higher voltages which cause X-ray radiation damage.
Accordingly, there is need for a triode sputtering system in which contamination from the undesired sputtering of interior surfaces is suppressed.
It should be noted also that triode systems are advantageous in that because a hot cathode supported discharge is used, lower gas pressures and, consequently, higher pumping speeds can be used during sputtering.